Sadly it sucks once you lvl main job its palace of the dead or dungeons if youre healer or tank. Potd floor floor 51-60 for about 45 hours and youre 60 and wanna kill yourself super boring.
PotD is by far the most efficient in both time and money as PotD uses it's own equipment so you can level from 1-60 and buy absolutely zero gear. The downside is exactly what is said here, it gets SUPER boring pretty fast.
That said, you can also do dungeons and roulettes, with Tanks and Healers obviously having shorter queue times, FATEs beast tribe quests once you unlock them (these are daily quests so can't be repeated ad nauseum in a day), side quests or PvP now.
Grinding levels is never any fun, but I will say the 1-50 grind is incredibly easy in PotD and the 50-60 grind is too, especially with another character already at 60 because or the armory bonus.